Benzene in blood as a biomarker of low level occupational exposure

Human biomonitoring of low-level benzene exposures

Historically, benzene has been widely used in a large variety of applications. Occupational exposure limits (OELs) were set for benzene as it was found to be acutely toxic, causing central nervous system depression at high exposures. OELs were lowered when it was discovered that chronic exposure to benzene could cause haematotoxicity. After confirmation that benzene is a human carcinogen causing acute myeloid leukaemia and possibly other blood malignancies, OEL were further lowered. The industrial application of benzene as solvent is almost completely discontinued but it is still used as feedstock for the production of other materials, such as styrene. Occupational exposure to benzene may also occur since it is present in crude oil, natural gas condensate and a variety of petroleum products and because benzene can be formed in combustion of organic material. In the past few years, lower OELs for benzene in the range of 0.05-0.25 ppm have been proposed or were already established to protect workers from benzene-induced cancer. The skin is an important potential route of exposure and relatively more important at lower OELs. Consequently, human biomonitoring - which integrates all exposure routes - is routinely applied to control overall exposure to benzene. Several potential biomarkers have been proposed and investigated. For compliance check of the current low OELs, urinary S-phenylmercapturic acid (S-PMA), urinary benzene and blood benzene are feasible biomarkers. S-PMA appears to be the most promising biomarker but proper validation of biomarker levels corresponding to airborne benzene concentrations below 0.25 ppm are needed.

Hsp70 overexpression in Drosophila hemocytes attenuates benzene-induced immune and developmental toxicity via regulating ROS/JNK signaling pathway

Benzene, a ubiquitous environmental chemical, is known to cause immune dysfunction and developmental defects. This study aims to investigate the relation between benzene-induced immune dysfunction and developmental toxicity in a genetically tractable animal model, Drosophila melanogaster. Further, the study explored the protective role of Heat Shock Protein 70 (Hsp70) against benzene-induced immunotoxicity and subsequent developmental impact. Drosophila larvae exposed to benzene (1.0, 10.0, and 100.0 mM) were examined for total hemocyte (immune cells) count, phagocytic activity, oxidative stress, apoptosis, and their developmental delay and reduction were analyzed. Benzene exposure for 48 h reduced the total hemocytes count and phagocytic activity, along with an increase in the Reactive Oxygen Species (ROS), and lipid peroxidation in the larval hemocytes. Subsequently, JNK-dependent activation of the apoptosis (Caspase-3 dependent) was also observed. During their development, benzene exposure to Drosophila larvae led to 3 days of delay in development, and ~40% reduced adult emergence. Hsp70-overexpression in hemocytes was found to mitigate benzene-induced oxidative stress and abrogated the JNK-mediated apoptosis in hemocytes, thus restoring total hemocyte count and improving phagocytotic activity. Further, hsp70-overexpression in hemocytes also lessened the benzene-induced developmental delay (rescue of 2.5 days) and improved adult emergence (~20%) emergence, revealing a possible control of immune cells on the organism's development and survival. Overall, this study established that hsp70-overexpression in the Drosophila hemocytes confers protection against benzene-induced immune injury via regulating the ROS/JNK signaling pathway, which helps in the organism's survival and development.

Exogenous 24-epibrassinolide enhanced benzene detoxification in Chlorophytum comosum via overexpression and conjugation by glutathione

Benzene, a hydrophobic xenobiotic, induces cell damage in both humans and plants. Due to its volatilization, benzene is an airborne environmental problem. The potential of an exogenous bioactive brassinosteroid phytohormone to enhance benzene removal for phytoremediation was investigated. Chlorophytum comosum had higher brassinosteroids content under benzene stress. Plant treated with 24-epibrassinolide (EBR) removed significantly more gaseous benzene than untreated plants under both light and dark conditions at an initial benzene of 12.75 μmol in the systematic chambers (P < 0.05). Although benzene increased malondialdehyde in plant tissue, EBR-treated plants lowered this lipid peroxidation by enhancing their antioxidant content and increasing benzene detoxification-related genes expression, including ascorbic acid (AsA), homogentisate phytyltransferase (HPT), and glutathione synthethase (GS). This contributed to maintaining higher photosynthetic performances. Moreover, EBR-treated plants had higher gene expression of ferredoxin-NADP reductase (FNR) and glucose-6-phosphate 1-dehydrogenase (G6PDH), thus promoting NADPH biosynthesis to cope with benzene under light and dark conditions, respectively. Further, higher glutathione biosynthesis promoted more glutathione conjugate of benzene products including S-phenylcysteine (SPC) in EBR-treated plants. Hence, application of exogenous EBR as foliar spray provided for enhanced benzene detoxification via antioxidant content, benzene detoxification-related genes and benzene conjugation products with glutathione (GSH) and consequently greater gaseous benzene removal.

Quantitative measurement of oxidative damage in erythrocytes as indicator in benzene intoxications

The metabolism of aromatic hydrocarbons by the organism forms products that cause cell death depending on the type of exposure. Benzene exposure has been linked to oxidative stress, hepatic damage, aplastic anemia, and hematopoietic cancer as lymphoid and myeloid leukemia. However, there are not fast methods to evaluate chronic benzene exposure in human blood. The objective of this work was the evaluation of the correlation between oxidative damage with benzene exposure and the level of cellular plasma membrane stability (CPMS) in erythrocytes to use it as a future indicator to determine the grade of benzene intoxications. CPMS in vitro assays were used to evaluate damage for benzene, toluene, and xylene. Erythrocytes CPMS assays in vitro shows a progressive reduction with benzene, toluene, and xylene suggesting that aromatic hydrocarbons complexity favors CPMS damage. Eight groups of Wistar rats (n = 5) were used to study the level of damage on CPMS by acute and chronic benzene administration. Enzymatic, metabolic, histological, and oxidative damage tests were performed. Acute administration (100 μL/100 g/single dose) showed a decrease of 66.7% in CPMS, while 63.6% for chronic administration (5 μL/100 g/every 2 days/3 months) showing a correlation with liver damage principally (transaminases activity increase, glycogen level decrease, and high oxidative damage). Tissue damage was observed in bone marrow, kidney, spleen, and lungs. Benzene produces damage on CPMS depending on the exposure time and dose. The CPMS technique could be used as an important aromatic hydrocarbons intoxication indicator.

Occupational health risk of working in garages: comparative study on blood pressure and hematological parameters between garage workers and Haramaya University community, Harar, eastern Ethiopia

Background

Occupational exposure to chemicals in garages causes a wide range of biological effects, depending upon the level and duration of exposure. In Ethiopia, there have been few studies conducted to assess the exposure of garage workers to chemicals. Preceding studies have not explored the effect of working in garage on blood pressure and hematological parameters. Therefore, this study aimed to assess differences in blood pressure and hematological parameters among garage workers compared to the Haramaya University community, Harar, eastern Ethiopia.

Materials and methods

A comparative cross-sectional study was conducted in Harar town, eastern Ethiopia. Thirty garage workers were selected and compared with 30 age- and sex-matched controls comprising of teachers and students. Demographic and occupational data were collected by using a structured questionnaire by a trained data collector. Blood pressure was measured using sphygmomanometry. Hematological parameters were measured with an automated hematology analyzer. Data were analyzed using Stata version 13.

Results

The majority of the garage workers did not implement effective preventive or control measures for workplace chemical exposure. Statistically significant increases were found in systolic (128.67±18.14 vs 106.33 ±9.27 mmHg, P<0.0001), diastolic blood pressure (90.33±11.29 vs 75.67 ±5.68 mmHg, P<0.0001), total white blood cells (7.9±1.51 vs 6.72±2.04×10⁹ cells/L, P=0.0138), and platelets (323.20±48.82 vs 244.1±47.3×10⁹ cells/L, P<0.0001) in garage workers compared to the control group. On the other hand, statistically significant decreases were found in red blood cells (5.13±0.38 vs 5.46±0.36×10¹² cells/L, P=0.0006), hemoglobin (14.89±0.71 vs 15.45±0.87 g/dL, P=0.0062), hematocrit (43.98%±1.99% vs 46.4%3±2.32%, P<0.0001), and mean corpuscular volume (83.19±2.93 vs 85.11±3.87 fL, P=0.0353) among garage workers compared to the control group.

Conclusion

There were significant differences in blood pressure and hematological parameters between garage workers and the control group. Therefore, appropriate and effective safety measures need to be taken by the workers to prevent possible chemical exposure during routine tasks.

Urinary Trans, Trans-Muconic Acid is Not a Reliable Biomarker for Low-level Environmental and Occupational Benzene Exposures

BACKGROUND

Benzene is a known occupational and environmental pollutant. Its urinary metabolite trans, trans-muconic acid (tt-MA) has been introduced by some environmental and occupational health regulatory associations as a biological index for the assessment of benzene exposure; however, recently, doubts have been raised about the specificity of tt-MA for low-level benzene exposures. In the present study, we investigated the association between urinary levels of tt-MA and inhalational exposure to benzene in different exposure groups.

METHODS

Benzene exposure was assessed by personal air sampling. Collected benzene on charcoal tube was extracted by carbon disulfide and determined by a gas chromatograph (gas chromatography with a flame ionization detector). Urinary tt-MA was extracted by a strong anion-exchange column and determined with high-performance liquid chromatography-UV.

RESULTS

Urinary levels of tt-MA in intensive benzene exposure groups (chemical workers and police officers) were significantly higher than other groups (urban and rural residents), but its levels in the last two groups with significant different exposure levels (mean = 0.081 ppm and 0.019 ppm, respectively) showed no significant difference (mean = 388 μg/g creatinine and 282 μg/g, respectively; p < 0.05). Before work shift, urine samples of workers and police officers showed a high amount of tt-MA and its levels in rural residents' samples were not zero.

CONCLUSION

Our results suggest that tt-MA may not be a reliable biomarker for monitoring low-level (below 0.5 ppm) benzene exposures.

Inhalation exposure or body burden? Better way of estimating risk--An application of PBPK model

We aim to establish a new way for estimating the risk from internal dose or body burden due to exposure of benzene in human subject utilizing physiologically based pharmacokinetic (PBPK) model. We also intend to verify its applicability on human subjects exposed to different levels of benzene. We estimated personal inhalation exposure of benzene for two occupational groups namely petrol pump workers and car drivers with respect to a control group, only environmentally exposed. Benzene in personal air was pre-concentrated on charcoal followed by chemical desorption and analysis by gas chromatography equipped with flame ionization detector (GC-FID). We selected urinary trans,trans-muconic acid (t,t-MA) as biomarker of benzene exposure and measured its concentration using solid phase extraction followed by high performance liquid chromatography (HPLC). Our estimated inhalation exposure of benzene was 137.5, 97.9 and 38.7 μg/m(3) for petrol pump workers, car drivers and environmentally exposed control groups respectively which resulted in urinary t,t-MA levels of 145.4±55.3, 112.6±63.5 and 60.0±34.9 μg g(-1) of creatinine, for the groups in the same order. We deduced a derivation for estimation of body burden from urinary metabolite concentration using PBPK model. Estimation of the internal dose or body burden of benzene in human subject has been made for the first time by the measurement of t,t-MA as a urinary metabolite using physiologically based pharmacokinetic (PBPK) model as a tool. The weight adjusted total body burden of benzene was estimated to be 17.6, 11.1 and 5.0 μg kg(-1) of body weight for petrol pump workers, drivers and the environmentally exposed control group, respectively using this method. We computed the carcinogenic risk using both the estimated internal benzene body burden and external exposure values using conventional method. Our study result shows that internal dose or body burden is not proportional to level of exposure rather have a non-linear relationship. At a higher exposure level such as for occupational exposure of petrol pump workers and drivers, the conventionally estimated risk is higher than risk estimated from internal body burden. Likewise, for environmental exposure the conventional risk estimation predict lower level than estimated in our study. This emphasizes the importance of body burden and to consider it as a key parameter while estimating health risk at varying level of exposure.

Hematological effect of benzene exposure with emphasis of muconic acid as a biomarker

Human exposure to benzene in work environment is a global occupational health problem. It is established that benzene requires to be metabolized to induce its effects. Benzene has been associated with various hematotoxins and carcinogens. The aim of this study was to investigate the effect of benzene on complete blood picture, with emphasis of trans, trans-muconic acid (t,t-MA) as a biomarker of benzene in urine, considering the influence of cigarette smoke. A total of 81 workers (61 males and 20 females) have been occupationally exposed to benzene. In addition, 83 workers (55males and 28 females) were also recruited as a control group. Complete blood picture was analyzed and urinary t,t-MA was determined by liquid chromatography. In addition, creatinine in the urine samples was determined. Levels of blood elements (white blood cells, red blood cells and platelets) were decreased among exposed workers compared with the controls. The urinary level of t,t-MA/creatinine of the exposed workers was elevated especially in the smoking group compared to the controls. This study recommends that complete blood picture and t,t-MA are helpful biomarker tests that should be done to detect the early effects of benzene exposure.

Hematological Evidence of Occupational Exposure to Chemicals and Other Factors among Auto-Repair Workers in Rawalpindi, Pakistan

Objectives

Occupational exposure to aromatic solvents causes many serious health hazards to workers, especially if an ambient environment increases the exposure during routine working hours. This study was conducted on two related groups, i.e., automobile mechanics (MCs) and automobile spray painters (PNs), with an effort to analyze effects of chemical exposure on hematological parameters, keeping a focus on environmental parameters and workers’ personal behavioral characteristics that could be held responsible for increasing exposure risk.

Methods

A preliminary survey of various chemicals used in these places was done, and 78 blood samples were collected from three groups (control, n = 24; mechanics, n = 25; painters, n = 29). Demographic features of workers were recorded through a short questionnaire.

Results

Results showed that mean red blood cell (RBC) count was lower both in MCs [t(51) = 2.38, p < 0.021, r = 0.32] and in PNs [t(47) = 2.12, p < 0.03, r = 0.29], whereas mean hemoglobin (Hb) was significantly lower in MCs [t(51) = 2.5, p = 0.017, r = 0.33]. Combined data for exposed groups for smokers (SMs) versus nonsmokers (NSs) showed that SMs had a significantly lower number (RBC count: t(52) = 2.28, p < 0.027, r = 0.25; Hb count: t(52) = 2.71, p < 0.009, r = 0.30] of these parameters than NSs, even compared to the control group. Moreover, logistic regression results showed that smoking is a significant predictor of reduction in RBC and Hb counts, besides occupational exposure and work experience to a little extent among exposed workers. Mean white blood cell count [t(47) = 2.63, p < 0.01, r=0.35], mean corpuscle volume [t(47)= –2.82, p = 0.007, r = 0.29], and packed cell volume [t(47)= –2.28, p = 0.027, r = 31] were higher exclusively in painters, which could be related to exposure to benzene in addition to isocyanate.

Conclusion

It appeared that workplace exposure may be complex due to interaction of multiple factors and PNs face much more exposure to isocyanate and aromatic solvents than MCs, which had significant effects on their hematopoiesis. Smoking enhances exposure risk manifolds, and among MCs it showed combined effects along with occupational exposure. There is a need to create awareness among these workers to adopt self-safety measures during routine tasks and also of a separate study to elucidate actual occupational exposure among them, eliminating confounding factors.

A calibrated human PBPK model for benzene inhalation with urinary bladder and bone marrow compartments

A physiologically-based pharmacokinetic (PBPK) model of benzene inhalation based on a recent mouse model was adapted to include bone marrow (target organ) and urinary bladder compartments. Empirical data on human liver microsomal protein levels and linked CYP2E1 activities were incorporated into the model, and metabolite-specific conversion rate parameters were estimated by fitting to human biomonitoring data and adjusting for background levels of urinary metabolites. Human studies of benzene levels in blood and breath, and phenol levels in urine were used to validate the rate of human conversion of benzene to benzene oxide, and urinary benzene metabolites from Chinese benzene worker populations provided model validation for rates of human conversion of benzene to muconic acid (MA) and phenylmercapturic acid (PMA), phenol (PH), catechol (CA), hydroquinone (HQ), and benzenetriol (BT). The calibrated human model reveals that while liver microsomal protein and CYP2E1 activities are lower on average in humans compared to mice, the mouse also shows far lower rates of benzene conversion to MA and PMA, and far higher conversion of benzene to BO/PH, and of BO/PH to CA, HQ, and BT. The model also differed substantially from existing human PBPK models with respect to several metabolic rate parameters of importance to interpreting benzene metabolism and health risks in human populations associated with bone marrow doses. The model provides a new methodological paradigm focused on integrating linked human liver metabolism data and calibration using biomonitoring data, thus allowing for model uncertainty analysis and more rigorous validation.

Bayesian algorithm implementation in a real time exposure assessment model on benzene with calculation of associated cancer risks

The objective of the current study was the development of a reliable modeling platform to calculate in real time the personal exposure and the associated health risk for filling station employees evaluating current environmental parameters (traffic, meteorological and amount of fuel traded) determined by the appropriate sensor network. A set of Artificial Neural Networks (ANNs) was developed to predict benzene exposure pattern for the filling station employees. Furthermore, a Physiology Based Pharmaco-Kinetic (PBPK) risk assessment model was developed in order to calculate the lifetime probability distribution of leukemia to the employees, fed by data obtained by the ANN model. Bayesian algorithm was involved in crucial points of both model sub compartments. The application was evaluated in two filling stations (one urban and one rural). Among several algorithms available for the development of the ANN exposure model, Bayesian regularization provided the best results and seemed to be a promising technique for prediction of the exposure pattern of that occupational population group. On assessing the estimated leukemia risk under the scope of providing a distribution curve based on the exposure levels and the different susceptibility of the population, the Bayesian algorithm was a prerequisite of the Monte Carlo approach, which is integrated in the PBPK-based risk model. In conclusion, the modeling system described herein is capable of exploiting the information collected by the environmental sensors in order to estimate in real time the personal exposure and the resulting health risk for employees of gasoline filling stations.

Solid phase microextraction as a short-term sampling technique for BTEX occupational exposure

Solid phase microextraction (SPME) has been widely used for many years in various applications, such as environmental and water samples, food and fragrance analysis, or biological fluids. The aim of this study was to suggest the SPME method as an alternative to conventional techniques used in the evaluation of worker exposure to benzene, toluene, ethylbenzene, and xylene (BTEX). Polymethylsiloxane-carboxen (PDMS/CAR) showed as the most effective stationary phase material for sorbing BTEX among other materials (polyacrylate, PDMS, PDMS/divinylbenzene, Carbowax/divinylbenzene). Various experimental conditions were studied to apply SPME to BTEX quantitation in field situations. The uptake rate of the selected fiber (75 microm PDMS/CAR) was determined for each analyte at various concentrations, relative humidities, and airflow velocities from static (calm air) to dynamic (> 200 cm/s) conditions. The SPME method also was compared with the National Institute of Occupational Safety and Health method 1501. Unlike the latter, the SPME approach fulfills the new requirement for the threshold limit value-short term exposure limit (TLV-STEL) of 2.5 ppm for benzene (8 mg/m(3)).

Long-lasting neurotoxicity of prenatal benzene acute exposure in rats

Benzene is a common element of environmental pollution. Although this substance is not recognized as a teratogenic agent, it is not known whether prenatal exposure to benzene may induce neurobehavioral changes in the progeny. Benzene 0.1mg/kg was injected subcutaneously (s.c.) acutely at day 15 of gestation into pregnant female rats of the Sprague-Dawley strain and neurotoxicity of the substance was studied in pups and male adult animals of the same progeny. No change was found in total number of neonates, body weight and eye opening time between benzene-exposed animals and controls. No malformations were observed. At birth, neonatal reflexes (cliff aversion, forelimb placing, bar holding, forelimb grasping, startle) were scored in benzene-exposed pups and their percent appearance was found to be anticipated (more benzene-exposed pups exhibited reflexes each day) in comparison to that of control animals. Also, the completion (maximum appearance, i.e. 100% of the brood was found to exhibit each reflex) of neonatal reflexes in benzene-exposed animals preceded that of controls. Starting 2 months after birth, cognitive and motor performance was assessed only in male animals of the prenatally benzene-exposed progeny. The overall evaluation of motor activity in benzene-exposed animals in the open-field test revealed reduced ambulation in these rats as compared to control animals. Acquisition of active avoidance responses in the shuttle-box test, as assessed by the number of conditioned avoidance responses and the percent of learners, was impaired in benzene-exposed rats as compared to control animals. Prenatal exposure to benzene was also followed by reduced retention latency in a step-through passive avoidance task in two retention tests. These results suggest that acute exposure to benzene during gestational organogenesis may cause long-lasting changes in motor behavior and cognitive processes. This may be relevant for the assessment of benzene toxic profile for the progeny of pregnant subjects, although teratogenic effects are not observed.

Environmental and occupational exposure to benzene in Thailand

Exposure to benzene in air is a concern in Thailand, particularly since it was observed that the incidence of blood-related cancers, such as leukemia and lymphoma, has increased in the past few decades. In Bangkok, the mean atmospheric levels of benzene on main roads and in schools were 33.71 and 8.25 ppb, respectively, while in gasoline service stations and petrochemical factories the mean ambient levels were 64.78 and 66.24 ppb, respectively. Cloth vendors (22.61 ppb) and grilled-meat vendors (28.19 ppb) working on the roadsides were exposed to significantly higher levels of benzene than the control group (12.95 ppb; p<0.05). Bangkok school children (5.50 ppb) were exposed to significantly higher levels of benzene than provincial school children (2.54 ppb; p<0.01). Factory workers (73.55 ppb) and gasoline service attendants (121.67 ppb) were exposed to significantly higher levels of benzene than control workers (4.77 ppb; p<0.001). In accordance with the increased benzene exposures, levels of urinary trans,trans-muconic acid (MA) were significantly increased in all benzene-exposed groups. In school children, the levels of MA were relatively high, taking into account the much lower level of exposure. Blood benzene levels were also significantly increased in Bangkok school children (77.97 ppt; p<0.01), gasoline service attendants (641.84 ppt; p<0.05) and factory workers (572.61 ppt; p<0.001), when compared with the respective controls. DNA damage, determined as DNA strand breaks, was found to be elevated in gasoline service attendants, petrochemical factory workers, and Bangkok school children (p<0.001). The cytogenetic challenge assay, which measures DNA repair capacity, showed varying levels of significant increases in the numbers of dicentrics and deletions in gasoline service attendants, petrochemical factory workers and Bangkok school children, indicating a decrease in DNA repair capacity in these subjects.

Rapid and sensitive static headspace gas chromatography–mass spectrometry method for the analysis of ethanol and abused inhalants in blood

A sensitive and specific method using static headspace gas chromatography coupled with mass spectrometry (GC/MS) has been developed for the quantitative determination of ethanol in biological fluids using n-propanol as internal standard. Gas chromatography was performed in isothermal mode with a GC run time of 2.6 min. The quantification was performed using scan mode abstracting a quantitative ion and a qualifier ion for ethanol and for the internal standard. The method was linear (r(2), 0.999, in the concentration range of 5-200 mg/dl), specific (no interference from methanol acetaldehyde, acetone or from endogenous materials), sensitive (limit of quantification and limit of detection of 0.2 and 0.02 mg/dl, respectively) and robust (less than 5% inter- and intra-assay coefficient of variation). A slightly modified method was also developed for the quantification of five commonly abused inhalants (dichloromethane, ethyl acetate, benzene, toluene and xylene) in blood. The method used a gradient GC program with a run time of 8 min. The quantification was performed using scan mode and integrating the area under the peak using trichloroethane as an internal standard. Without optimization, the method was linear (from 5 to 100 mg/l) and sensitive.

Environmental and biological monitoring of occupational exposure to organic micropollutants in gasoline

An exposure risk assessment of workers in a refinery production unit was undertaken. Gasoline and its main components were investigated through environmental and biological monitoring. Measured variables were environmental benzene, toluene, pentane and hexane; benzene and toluene in blood and urine; tt-MA (metabolite of benzene) in urine. Multivariate statistical analysis of the data showed that worker's exposure to the above substances fell within the limits specified by organisations such as ACGIH. Also, biological values complied with reference values (RV) for non-occupationally-exposed population. Different values of biological variables were determined by separating smokers from non-smokers: smokers had hematic and urinary benzene values significantly higher than non-smokers. During a 3-yr sampling, it was possible to identify a significant decrease of benzene in the workplace air and of hematic benzene for non-smokers. The most exposed department, one in which tank-lorries were loaded, needs further investigation and extended monitoring.